1. Field of the Invention
The present invention relates to a method for repairing cementitious surfaces and, in particular, to repairing concrete surfaces. The present invention also relates to polymerizable compositions for repairing such surfaces and, more particularly, to polymerizable urethane compositions useful in repairing such surfaces.
2. Description of the Prior Art
With the ever increasing amount of traffic on roads and highways it has been found increasingly important to effect quick and efficient road repairs which will have a long service life. Various polymeric compositions have long been used as sealants and crack fillers for structural and road surface concrete. However, many of these compositions have been found better suited for repairing traditional materials, such as asphalt solvent systems. There have been attempts to repair cement or concrete surfaces with urethane compositons. For example, U.S. Pat. No. 3,723,163 discloses a one-part urethane composition for sealing cracks in cement surfaces and U.S. Pat. No. 4,275,172 discloses urethane formulations which are frothed with an inert gas and which are applicable to patching concrete.
A problem arises in the use of urethane compositions, however, as there is a tendency for bubbles to form in the polyurethane. This bubble formation is caused by the reaction of the polyurethane prepolymer or monomer isocyanate groups when water is present in the surface to be repaired. The art attempts to reduce this bubble formation or foaming by minimizing the amount of water present which can react with the isocyanate groups.
It is thus seen that although polymeric compounds have long been used as sealants and crack fillers, there have been problems associated with the use of quick-setting urethane compositions for concrete surfaces because such compositions are very reactive with water. The problems are especially exacerbated when concrete or cement is to be repaired because of the porous nature of the substrate, which may contain relatively large amounts of water.
In an attempt to overcome these problems of using polymerizable urethane compositions in the presence of water, the art has attempted, for example, to utilize water absorbing materials to offset the reaction of the isocyanate groups with water. This method has been suggested in the aforementioned U.S. Pat. No. 4,275,172. Another method for offsetting this reaction is to prime the surface to be repaired, such as suggested by the aforementioned U.S. Pat. No. 3,723,163. Even when the art utilizes an isocyanate-water reaction, it has been found beneficial to minimize foaming. For example, U.S. Pat. No. 4,139,676 discloses the consolidation of an aggregate material by means of an isocyanate-terminated prepolymer. Yet even though the isocyanate terminated prepolymer reacts with water present in the aggregate, the patent discloses the desire to minimize foaming by using an aggregate having a low moisture content.
The problems encountered in using these urethane systems are due to the extremely reactive nature of such compositions with water. Water contamination of these systems, e.g., due to the presence of surface moisture, often leads to a degradation of the polymer matrix structure and a shortening of the polymeric chains. These effects lead to a polymer matrix having a reduced tensile strength and reduced elasticity, thereby resulting in an early failure of the repair. A polymeric system which can overcome these problems would be a most useful and welcome system in the art.
In view of the foregoing, it is an object of the present invention to provide a method and composition for repairing cementitious surfaces which constructively utilizes water present in the polymerization reaction environment.
It is a further object of the present invention to provide repairs of cementitious surfaces which have a longer service life than those previously used.
It is also an object of the present invention to provide repairs of cementitious surfaces with compositions which foam during polymerization due to water present in the reaction environment.
It is yet another object of the present invention to provide such foams for repairing cementitious surfaces which maintain full tensile and bonding strength and which retain elas- ticity.
It is still another object of the present invention to provide such foams which are useful in repairing cementitious surfaces in the absence of moisture absorbing materials.
These and other objects as well as the scope, nature and utilization of the invention, will be apparent to those skilled in the art from the following description and the appended claims.